In 1934, during one of Steve's many attempts to escape from The Keep, he was convinced to stay by Daniel Whitehall, the Kraken, who encouraged Steve to prove himself and embrace Hydra's beliefs, to value collectivism over individualism and to pursue the leadership of the strong.
"In the universe you know, Steve Rogers was transformed from a skinny kid from Brooklyn into the First Avenger, Captain America by the Super-Soldier Serum. However, in this universe, Steve is injured and instead must fight Hydra in a suit of armor created by Howard Stark. Here he is called "The Hydra Stomper"."
After gaining power from the serum Schmidt became the Red Skull and decided to make Hydra into its own power and try to take over the entire world using a powerful gun harnessing the power of the Tesseract (Captain America.)
HYDRA was an authoritarian-subversive paramilitary terrorist organization bent on world domination. It was founded in ancient times, formerly as a cult dedicated to the fanatical worship of Hive, a powerful Inhuman that was exiled to the planet Maveth by ancient Inhumans.
Alexander Pierce's devotion to order swayed him to join Hydra's silent ranks hidden within various state organizations and S.H.I.E.L.D. He eventually became the top-ranking member of Hydra, and developed a decades long plot to destroy S.H.I.E.L.D. from within, and in the process gaining total control over the world.
Toby Jones on Steve Rogers (Captain America) Joining Hydra
Why did Captain America join Hydra?
In 1934, during one of Steve's many attempts to escape from The Keep, he was convinced to stay by Daniel Whitehall, the Kraken, who encouraged Steve to prove himself and embrace Hydra's beliefs, to value collectivism over individualism and to pursue the leadership of the strong.
Jonathan "John" Garrett was a turncoat S.H.I.E.L.D. agent who joined HYDRA after being refused aid by S.H.I.E.L.D. when he was injured during a mission in Sarajevo. He survived his injury by becoming the first subject of the Project Deathlok.
The Hydra experimentation on Barnes causes him to survive his fall, and he is recaptured by the Hydra wing of the Soviet Union, where he is tortured and brainwashed by Arnim Zola and turned into the Winter Soldier, a mind-controlled super soldier with a metal prosthetic arm.
When Erskine refused to hand it over, however, Schmidt took it by force and injected himself, only to discover that it was incomplete, resulting in Schmidt's face becoming hideously disfigured while he gained his abilities. Schmidt's skin was burned off his face, giving him the nickname of the Red Skull.
One of the Nazi members, Baron Wolfgang von Strucker, quickly seized control of the Hydra organization and restructured it to be dedicated to world domination through terrorist and subversive activities on various fronts, resulting in a global neo-fascist New World Order.
In 2016, Captain America brought comic books to the forefront of national discussion with a single phrase: “Hail Hydra.” These two words proclaimed Captain America's allegiance to Hydra, one of Marvel Comics most recognizable villains which has historically been used as an allegory for the Nazi Party.
Red Skull was cursed to become the guardian of the Soul Stone for over seven decades, rendering him unable to leave the planet throughout these years, only able to advise those who came onto the planet seeking the Soul Stone.
Having some of the most evil villains in history among its ranks, Hydra has been wreaking havoc around the globe since World War II. To combat this threat, S.H.I.E.L.D. rose up as its equal, but opposing, organization.
A cowardly young man, Bob was persuaded into joining the criminal organization HYDRA by his wife, Allison, who accused him of not being able to hold a steady job. The thought of a stable career with a dental plan also appealed to Bob, though he was disappointed to find out HYDRA does not offer full dental like A.I.M..
It's also what he wanted for Steve. Like anybody that ends up traumatized by a war experience, he was affected by it for the rest of his life. So, what felt like a desire there was for a restart - for him and for Steve in a way. It didn't necessarily feel like the shield was gonna be that.
In 2014's Captain America: The Winter Soldier, it is revealed that Stephen Strange was on a Hydra hit-list because he could interfere with their future plans, even though he was practicing medicine at the time and has no current connection to magic - an apparent plot hole.
Mainly due to his Nazi ties, Red Skull is shown to be so depraved and horrible that even other villains are disgusted by him, such as Kingpin, Doctor Doom (who is of Roma descent), Magneto (who is a Holocaust survivor) and even the Joker, who is also Pure Evil (although their encounter was non-canon).
Thanos would dominate the Red Skull in just about every scenario. While Johann Schmidt may have the advantage in a scenario where he has a Cosmic Cube or Kobik and Thanos has nothing to counter it, even then Thanos would likely find a way to win the day.
However, Red Skull saw his true intentions, informing Gamora that Thanos was, in fact, weeping for Gamora, as he truly loved her as a daughter, and was heartbroken that he had to sacrifice her to get the Soul Stone. Disbelieving, Gamora could not comprehend that Thanos ever showed genuine love for her.
Bucky Barnes, like Steve Rogers, has lived for several decades due to cryogenic freezing and the super-soldier serum. Bucky's life expectancy could potentially surpass Steve's 116 years, depending on circumstances. Despite outwardly aging at the same rate as Steve, Bucky can still live for at least another 80 years.
While in the MCU Stucky fans ship them romantically, among comic fans their relationship is viewed very differently. In Marvel's canon Prime Universe in the comics, Earth-616, Bucky and Steve have a father-son relationship.
James Buchanan “Bucky” Barnes enlists to fight in World War II, but eventually literally falls in battle. Unfortunately, the evil Arnim Zola recovers him and erases his memory, turning him into a highly-trained assassin called the Winter Soldier.
Years later, in an effort to help purge their country of strife, the twins joined HYDRA and agreed to undergo experiments with the Scepter under the supervision of Baron Strucker, with the Mind Stone awakening and amplifying Wanda's powers.
Grant Ward was actually placed undercover at Hydra. He was supposed to get close enough to leadership to report back to SHIELD. Unfortunately, Ward found himself agreeing with some of the very people he was sent in to investigate. He ended up leaving SHIELD and joining Hydra for real.
